Method for operating an internal combustion engine utilizing a carbohydrate-based fuel mixture

ABSTRACT

A method for operating an internal combustion engine utilizing a fuel mixture containing a suspension in air at a concentration of about 200 mg of fuel per liter of air, of a solid fuel including at least one of a cereal flour, a cotton flour, a soybean flour, a potato flour, a cassava flour, a dehydrated chocolate powder and a dehydrated milk powder, the solid fuel being in the form of a powder having an average particle diameter and median particle diameter at least 150 μm.

This application is a division of Ser. No. 10/297,623 filed Dec. 17,2002, incorporated herein by reference, which is a filing under 35 USC371 of PCT/FR01/01905, filed Jun. 19, 2001.

The invention relates to a solid fuel and a fuel mixture containing it.

The fuels most widely used at the present time for producing energy,particularly in internal combustion engines, are derived from the oil orgas industry.

However, depletion of the world resources of oil and gas products iscausing problems of supply and cost.

Furthermore, the use of these fuel sources is giving rise to numerousproblems of environmental pollution.

To overcome this problem, it was proposed to use catalytic convertersand particle filters, which add to the manufacturing cost of the vehicleor other equipment running on this type of fuel.

It was then proposed to use nuclear energy or solar energy.

However, this gives rise to problems of environmental pollution andenvironmental safety and their use in engine-driven vehicles,particularly motor vehicles and aeroplanes, comes up against problems ofstorage, transport and hence cost.

Also, the risk of explosion of cereal grain dust in grain silos has beenknown for many years.

In fact, cereal grains produce dust which is highly explosive in contactwith air. This high explosiveness of cereal grain dust in silos has beenexplained by their average particle size, which is below about 75 μm.Thus, when this cereal grain dust is suspended in a large amount of airin the presence of gases derived from fermentation of the cereal grains,the mixture of cereal grain dust, air and fermentation gases becomesexplosive.

The object of the invention is to provide a fuel which is an alternativeto the fuels derived from the oil, gas, nuclear or solar industry, whosetransport or storage presents no difficulties, whose use produces notoxic waste and which is readily available and renewable.

For this purpose the invention proposes a solid fuel containingpredominantly at least one constituent which in turn contains mainly atleast one compound selected from the group comprising starch, lactose,cellulose and derivatives thereof, and at least 15% by weight ofcarbohydrates, based on the total weight of the constituent(s), theconstituent(s) being in the form of a powder whose average particlediameter and median particle diameter are greater than or equal to 150μm and preferably between 150 and 500 μm.

Preferably, at least about 70% by volume of said powder consists ofparticles with a diameter greater than or equal to 150 μm.

In a first embodiment of the fuel of the invention, said fuel is totallycomposed of said at least one constituent.

A particularly preferred solid fuel of the invention is one in whichsaid at least one constituent is (are) selected from the groupcomprising a cereal flour, cotton flour, soybean flour, potato flour,cassava flour or tapioca, dehydrated chocolate powder, dehydrated milkpowder and mixtures thereof.

If said at least one constituent is a cereal flour, the cereal ispreferably wheat, rye, rice, maize, barley, sorghum, foxtail, millet,oats, bran, corn dredge, triticale, buckwheat or mixtures thereof.

In one preferred embodiment of the invention, said at least oneconstituent is cotton flour.

In another preferred embodiment of the invention, said at least oneconstituent is soybean flour.

Another flour which is particularly appropriate as a fuel of theinvention is potato flour.

Yet another flour which is appropriate as a fuel of the invention istapioca.

The solid fuel of the invention can also consist of dehydrated chocolatepowder.

In yet another embodiment of the invention, the solid fuel of theinvention consists of dehydrated milk powder.

Particularly preferably, the solid fuel of the invention consists of amixture of two or more of said at least one constituent.

The invention further proposes a fuel mixture composed of the fuel ofthe invention suspended in air at a concentration of about 200 mg offuel per liter of air.

The invention will be understood more clearly and other objects,characteristics, details and advantages thereof will become more clearlyapparent from the following explanatory description referring to theattached Figures, in which:

FIG. 1 is a diagrammatic side view of a commercial lawn mower;

FIG. 2 shows an enlarged section of the part marked II in FIG. 1,modified to run on the fuel of the invention;

FIG. 3 shows the particle size curve, measured with a Coulter LS lasergranulometer, of a commercial dehydrated chocolate powder used inExample 1;

FIG. 3 bis shows the particle size curve of FIG. 3 in the form ofnumerical values;

FIG. 4 shows the particle size curve, measured with a Coulter LS lasergranulometer, of a commercial dehydrated milk powder used in Example 2;

FIG. 4 bis shows the particle size curve of FIG. 4 in the form ofnumerical values;

FIG. 5 shows the particle size curve, measured with a Coulter LS lasergranulometer, of a fine middlings fraction of a wheat flour used inExample 3;

FIG. 5 bis shows the particle size curve of FIG. 5 in the form ofnumerical values;

FIG. 6 shows the particle size curve, measured with a Coulter LS lasergranulometer, of a coarse middlings fraction used in Example 4;

FIG. 6 bis shows the particle size curve of FIG. 6 in the form ofnumerical values;

FIG. 7 shows the particle size curve, measured with a Coulter LS lasergranulometer, of a coarse middlings fraction used in Example 5; and

FIG. 7 bis shows the particle size curve of FIG. 7 in the form ofnumerical values.

The high explosiveness of cereal grain dust has always been consideredto be the result of three factors:

-   -   the particle size of the dust, the average particle diameter        being below about 75 μm;    -   the presence of gases originating from the fermentation of the        grains themselves; and    -   the presence of a large volume of air in which the dust        particles are suspended.

However, this explosiveness phenomenon has never been reported orstudied for the flours obtained industrially by grinding of the cerealgrains themselves.

It has now been discovered, surprisingly, that cereal flour whoseaverage particle diameter and median particle diameter are greater thanor equal to 150 μm, and preferably between 150 and 500 μm, can be usedas a solid fuel for running internal combustion engines in particular,and can thus replace oil or gas products.

This is particularly surprising and goes against a prejudice of theprior art.

The fact that cereal grain dust has a high explosiveness has neveractually been considered as a reason for cereal grains being goodfuels—quite the opposite.

Their good fuel quality is due first and foremost to the fact that, inthe absence of turbulence, i.e. under laminar flow conditions, with arichness of 1, i.e. with a stoichiometric fuel:air ratio of 1:1, and atatmospheric pressure, the flame propagation velocity of hydrocarbons isabout 0.4 m/s whereas that of edible cultivated flours is about 30 m/s.

Now, in an engine, the piston/valve device has the characteristic ofincreasing the turbulence in the combustion chamber almost in proportionto the speed of rotation of the engine.

This results in an increase in the combustion velocity.

In the case of hydrocarbons the combustion is combustion by deflagrationand has a velocity of 20 m/s, whereas in the case of edible cultivatedflours it is combustion by detonation, which is a characteristic ofexplosives, and can have a velocity of as much as 2000 m/s.

Now, in an engine, the propagation of an explosive wave causes theformation and propagation of shock waves, which propagate in the burntor as yet unburnt gases.

On the one hand, these shock waves, which are detected by a loudpinging, drumming or knocking, have the effect of reducing the power ofthe engine and accelerating its wear. On the other hand, when they arediffracted or reflected, very high temperatures may be generated.

Thus, as regards their high combustion velocities under turbulent flowconditions, everything suggests that edible cultivated flours areinappropriate for use as fuels, particularly in internal combustionengines.

In addition, any product that appears a priori to be appropriate as agood fuel must have other physical and thermodynamic characteristics,namely, inter alia, compressibility or compression ratio, while at thesame time having an acceptable self-ignition temperature, minimumignition energy, enthalpy, volatility and frost resistance.

In fact, it is of interest to increase the compression in order toincrease the thermal efficiency of an engine and, in all types ofengine, there is a compression phase which heats the air or air/fuelmixture to a high temperature before the ignition/combustion phase. Now,when a gas is compressed, its temperature increases.

Thus, in a controlled ignition engine, the compression ratio is veryquickly limited by the self-ignition of the intimate air/fuel mixture.This intimate air/fuel mixture is sucked into the cylinder and thencompressed by the piston. The temperature at the end of the compressionphase of the air/gasoline mixture is about 194° C. In this type ofengine, everything is done to avoid self-ignition by compression.

Conversely, in a compression ignition engine or diesel engine, only theair is sucked into the cylinder and then compressed by the piston in aratio that is at least twice as high as in the controlled ignitionengine. The fuel is injected into the combustion chamber at the end ofcompression. This results in self-ignition of the diesel fuel in contactwith the air, heated to a temperature of about 500° C.

Consequently, in contrast to the case of a controlled ignition engine,self-ignition in the case of a compression ignition engine is caused bycompression.

Thus, in order to be able to replace gasoline or diesel fuel, theproduct put forward as a fuel must have a self-ignition temperatureabove 194° C. for use in a controlled ignition engine, and below 500° C.for use in a compression ignition engine.

Now, there is nothing in the prior art to indicate that ediblecultivated flours are capable of fulfilling one of these requirements,let alone both.

Nevertheless, in the invention, the minimum ignition temperature ofclouds of edible flours was determined experimentally in aGodbert-Greenwald furnace and it was then discovered that the minimumignition temperatures are between 350° and 500° C.

Therefore, edible cultivated flours can replace gasoline are capable notonly of replacing gasoline, but also of withstanding higher temperaturesand hence higher compression ratios, which helps to increase theefficiency of the controlled ignition engine.

As far as the compression ignition engine is concerned, again they arecapable of replacing diesel fuel advantageously.

The minimum ignition energy is the smallest amount of energy that has tobe applied to a fuel in order to ignite it when it is mixed with air. Itis often characterized by the energy of the spark of a capacitivedischarge. Now, there is nothing in the prior art that suggests ordiscloses that the minimum ignition energy of edible cultivated floursis comparable to that of gases.

It has now been discovered that the lowest minimum ignition energy ofedible cultivated flours is in the order of a millijoule, i.e. similarto that of gases. This minimum ignition energy of edible cultivatedflours was determined experimentally in a Hartmann igniter.

Furthermore, liquid hydrocarbons such as gasoline, diesel fuel andkerosene have a specific calorific value, or enthalpy, of about 43MJ/kg, whereas edible cultivated flours have a specific calorific valueof only about 15 MJ/kg.

Here again, this thermodynamic property of edible cultivated flourssuggests that they are not appropriate as heat engine fuels.

This is not the case at all.

In fact, the calorific value of 1 liter of a detonating mixtureconsisting of air and gasoline is 760 calories, whereas it has now beendiscovered that the calorific value of 1 liter of a detonating mixtureconsisting of air and flour is 703 calories.

Compared with gasoline, more than twice the amount of flour is burnt forthe same volume of air. The stoichiometric ratio is 15.1 grams of airper gram of gasoline and 6.5 grams of air per gram of flour, i.e. astoichiometric ratio equivalent to methanol.

Furthermore, as the basic motorized system is modified very little, theconsumption ratio for the equivalence calculation simply corresponds tothe ratio of the calorific values:1 liter of gasoline=43 MJ×0.7 (density of gasoline)=30 MJ1 liter of flour=15 MJ×0.5 (density of edible cultivated flour)=22.5 MJConsequently, 1.3 liters of flour are equivalent to 1 liter of gasoline.

As far as the frost resistance of edible cultivated flours is concerned,since said flours naturally contain about 15% by weight of water, thereis every likelihood that they crystallize at a temperature below 0° C.As a result of this crystallization, they would lose their fluidity andform one or more compact and indissociable blocks.

Now, this is not the case: edible cultivated flours (tested to −20° C.)have a frost resistance not possessed by certain liquid fuels such asdomestic fuels and gasoline, whose freezing points are −9° C. and −18°C. respectively.

Furthermore, they retain their fluidity at this temperature.

The value of an internal combustion engine fuel also depends on itsvolatility.

The volatility of a fuel is characterized by its density.

Now, where the density of gasolines is 0.7 and that of diesel fuels andkerosenes 0.8, the density of edible cultivated flours is 1.5.

Once again, this physical characteristic of edible flours does not augurin favor of their use as fuels.

However, as edible cultivated flours are pulverulent solids that are notconverted to a gas phase for combustion, they are not subject to thewell-known detrimental phenomenon of vaporlock exhibited by liquidfuels; this is one of their advantages.

Other physical characteristics of edible cultivated flours are such thatthe latter are dismissed by those skilled in the art of fuels.

In fact, in contrast to liquid hydrocarbons, edible cultivated floursare miscible with water and actually have a natural water content of upto 15% by weight, based on their total weight. This high water contentlowers their calorific value and their combustion velocity while at thesame time increasing their requisite minimum ignition energy.

Also, water increases the viscosity of edible cultivated flours andhence decreases the fluidity and volatility of the particles, which,depending on the degree of hydration, can go as far as a pasty amalgam(lumps) and even a very liquid consistency capable of stopping theengine.

Furthermore, the particles present in the powder formed by ediblecultivated flours have a strong cohesion which gives rise to aphenomenon of agglomeration and sticking/adhesion on the walls of thereceptacle containing them.

Thus, the greatest difficulties are to be anticipated when ediblecultivated flours flow from the tank containing the fuel to the pointwhere this fuel mixes with air.

Once again, this physical characteristic does not augur in favor of theuse of edible cultivated flours as fuels.

Now, all these prejudices of the prior art and the problems mentionedabove have been solved by the invention, which is based on the principleof choosing the particle sizes of the edible cultivated powdersconstituting the fuel of the invention.

In fact, choosing an edible cultivated powder with a particle size, i.e.an average diameter and a median diameter, greater than or equal to 150μm, and preferably of between 150 and 500 μm, makes it possible tocontrol the combustion velocity: increasing the size of the particles ofedible cultivated powders decreases the surface area in contact withatmospheric oxygen, which is the oxidant. This results in a reduction inthe oxidation rate.

Furthermore, the ash content, i.e. the content of minerals such aspotassium, magnesium, calcium, phosphorus and sodium, in the ediblecultivated powders constituting the fuel of the invention also acts asan anti-knock agent, like the lead tetraethyl formerly added to gasolineand now replaced by benzene and potassium.

In the same way, choosing this specific particle size solves the problemassociated with their natural water content and the strong cohesionbetween the particles.

In fact, the amount of water absorbed and the rate of absorption by theparticles of the edible cultivated powders of the invention decreaseswith the size of the particles.

Now, because of their high stability, storage of the flours requires nomore precautions than that of liquid fuels, which are themselvessensitive to water.

As regards the problem of cohesion between the particles that results inthe phenomenon of agglomeration, this problem can be surmounted bygenerating a vibration, as described below.

The average and median diameters of the solid fuels of the inventionwere measured by the COULTER laser method of particle size measurementon a Coulter LS apparatus.

The average diameter is the diameter calculated by the apparatus'software and represents the average diameter of the particles whose sizeis measured.

The median diameter corresponds to the particle size at which 50% byvolume of the particles constituting the sample whose size is measuredare smaller and 50% by volume of the particles constituting the samplewhose size is measured are larger.

The more similar the average diameter and median diameter, the more thepowder whose particle size is measured is homogeneous, i.e. has a singlepopulation.

In fact, the particle size distribution of the powder constituting thefuel of the invention is also an important criterion.

Preferably, the size distribution of the particles constituting thestate of the invention is narrow, i.e. the fuel contains the smallestpossible number of different particle size populations. This means that,in the fuel of the invention, more than 70% by volume of the particlesconstituting the powder must have a diameter greater than or equal toabout 150 μm.

The term “flour” is understood here as meaning the flour producedindustrially and used at the present time e.g. in the bakery industry.This flour can be used directly as fuel, without further conversion ortreatment.

For example, it can be used to run internal combustion engines, whetherof the controlled ignition type or diesel type, to run turbines andboilers, e.g. central heating boilers, and also to run industrialfurnaces.

The composition of cereal flours varies according to the cereal and itscultivation conditions. It also depends on the grinding method used andthe amounts of any additives introduced.

The cereal flours currently on the market contain predominantly starch,i.e. more than 70% of starch, water, proteins and a very smallproportion of fats.

Thus the cereal flours used, which are usable as fuels according to theinvention, contain predominantly starch and at least 15% by weight ofcarbohydrates.

Furthermore, these flours have an average particle diameter whoseaverage diameter and median diameter are greater than or equal to 150 μmand preferably between 150 and 500 μm.

The particularly preferred flours are those in which more than 70% byvolume of the particles have a diameter greater or equal to 150 μm.

The cereal flours used and tested in the invention are the flours ofwheat, rye, rice, maize, barley, sorghum, foxtail, millet, oats, bran,corn dredge, triticale or buckwheat.

Some of these industrial flours currently on the market can have anaverage particle diameter and a median particle diameter below 150 μm.

The invention therefore has an additional advantage associated with theproduction cost of the flours which can be used as fuels of theinvention.

In fact, to produce flours with an average particle diameter and amedian particle diameter greater than or equal to 150 μm, and preferablyof between 150 and 500 μm, the grain grinding and screening process forobtaining the conventional industrial flour can be stopped at an earlierstage.

The process for the production of the flours of the invention istherefore shorter and consequently more economic.

Also, it will be possible to use fractions obtained during flourproduction which would normally have been rejected because their averageparticle size was inappropriate for use in the food industry.

It has also been discovered that, surprisingly, other pulverulentindustrial products in common use can be employed as fuels provided thatthey contain predominantly starch or cellulose, or a derivative thereof,and at least 15% by weight of carbohydrates, and that the averageparticle diameter and median particle diameter of the powder of theseproducts are greater than or equal to 150 μm and preferably between 150and 500 μm.

Said pulverulent products are cotton, soybean, potato and cassavaflours. Cassava flour is commonly called tapioca.

Just as surprisingly, it has further been discovered that it is alsopossible to use dehydrated chocolate powder and dehydrated milk powder,which contain predominantly lactose or a lactose derivative and at least15% by weight of carbohydrates, and whose average particle diameter andmedian particle diameter are greater than or equal to 150 μm andpreferably between 150 and 500 μm.

Thus the invention is based on the surprising discovery that powders ofcommonly consumed natural products whose average particle diameter andmedian particle diameter are greater than or equal to 150 μm andpreferably between 150 and 500 μm, and which contain predominantly atleast one compound selected from the group comprising starch, a starchderivative, cellulose, a cellulose derivative, lactose, a lactosederivative and mixtures thereof, and at least 15% by weight ofcarbohydrates, constitute an excellent solid fuel.

The fuel of the invention can consist of a single powder, for examplecotton flour on its own, but it can also be a mixture of two or moredifferent powders, for example cotton flour plus soybean flour or cottonflour plus dehydrated milk powder.

It will be preferable to use a mixture of at least two flours withdifferent average particle diameters and median particle diameters,because the combustion of the smallest flour particles will initiate thecombustion of the larger particles.

Moreover, mixtures of several types of powders of different particlesize and calorific value afford the desired thermodynamics and also makeit possible to reduce the price of the fuel by mixing an inexpensivepowder with a more expensive flour, as is the case for potato flourmixed with dehydrated chocolate powder.

The fuel of the invention can be used on its own or in a mixture withother fuels.

However, the fuel of the invention is not an additive for another fuel.It is well and truly a fuel in itself.

Because it consists of cereal, cotton, soybean or potato flour ordehydrated chocolate or dehydrated milk powder, this fuel does notproduce any noxious discharges on combustion.

By way of example, wheat flour consists on average of 73.5% by weight ofstarch, 14.8% by weight of water, 10.8% by weight of proteins and 0.8%by weight of fats.

The combustion of wheat flour starch in the presence of air, i.e.essentially oxygen and nitrogen, discharges CO₂, water and nitrogen intothe atmosphere. The combustion of proteins discharges water, CO₂, SO₂,nitrogen and traces of SO₃, NH₃ and NO_(x).

Thus it is seen that the combustion of a wheat flour will producepredominantly water and nitrogen and about 18% of CO₂, which arenon-toxic products. The amounts of SO₃, NH₃ and NO_(x) produced by thecombustion of such a flour are negligible.

The fuel of the invention is to be used as a suspension in air toproduce a fuel mixture. The preferred proportion of fuel of theinvention per liter of air is about 200 mg of fuel of the invention perliter of air.

The calorific value of one liter of the fuel mixture of the invention,when the fuel is wheat flour, is 703 calories. By way of comparison, thecalorific value of one liter of air/gasoline mixture is 760 calories.

Thus, although the energy value of the fuel mixture of the invention isslightly less than that of gasoline (by 8%), it is neverthelessperfectly appropriate.

The discharges produced by combustion of the fuel mixture of theinvention contain no lead, benzene, sulfur, hydrocarbons or carbonmonoxide and a negligible amount of nitrogen oxides or solid particles.

The fuel of the invention can be used in modern internal combustionengines without major modification. Its calorific value is such that oneliter of gasoline will have to be replaced in modern vehicles by about1.3 l of fuel according to the invention.

It is seen from the above that the fuel of the invention has numerousadvantages. It is economically more advantageous than oil products andliquefied gases, it is available in abundance and it is an indefinitelyrenewable source of energy. It is biodegradable, has a neutralgreenhouse effect and is easy to store.

In fact, although the composition of the combustion discharges of ediblecultivated flours includes CO₂, in the same way as liquid hydrocarbons,combustion of the powders of edible cultivated products as defined inthe invention serves only to restore the CO₂ absorbed during the growthof the plants from which they are derived; this is in contrast toproducts of fossil origin, which massively shift the earth's carbonreserves into the atmosphere as carbon dioxide. Combustion of the fuelof the invention is therefore neutral in terms of the greenhouse effect.

Furthermore, the handling of the fuels of the invention presents nodanger to humans. In fact, as the fuel of the invention consists ofparticles whose average diameter and median diameter are greater than orequal to 150 μm, there is no risk of this fuel exploding in the event ofa violent shock.

Because it consists of edible products, the fuel of the invention alsopresents no danger when inhaled or ingested.

Another advantage of the invention is that, by mixing the differentpowders described here, it is possible to choose the odor released oncombustion.

To provide a clearer understanding of the subject of the invention,several modes of carrying out the invention will now be described by wayof purely illustrative and non-limiting Examples.

EXAMPLES

The experiments using the fuel of the invention were performed on acommercial lawn mower originally running on gasoline, as shown in FIG.1.

As seen in FIG. 1, this lawn mower is equipped with a gasoline tankmarked A, located above the carburetor, which gravity-feeds thecarburetor with gasoline. The lawn mower engine runs under constant flowconditions and the grass cutting blade, marked 6 in FIG. 1, engagesdirectly with the mower engine. Each rotation of the cutting blade 6thus corresponds to one rotation of the engine.

Few modifications were made to run the engine on the fuel of theinvention.

Only the fuel tank and the part where the fuel is sucked into thecarburetor were modified on this lawn mower.

These modifications are shown in FIG. 2, which is an enlarged view ofthe part marked II in FIG. 1. As shown in FIG. 2, in which theunmodified carburetor of the commercial lawn mower is marked 7, the airfilter of the commercial lawn mower has been removed and replaced with abent tube, marked 1 in FIG. 2, made of a rigid material such as metal orPVC.

At one of these ends, this bent tube 1 is joined to the air intake ofthe carburetor 7 by a connector, marked 5 in FIG. 2, made of a flexiblematerial.

The other end of the bent tube 1 is joined to the tank, marked 2 in FIG.2, by a connector 4, the tank 2 containing the powdered fuel of theinvention, marked 3 in FIG. 2.

This tank 2 is open at its top end to allow a permanent air supply, andis fitted at its bottom end with a perforated plate, marked 8 in FIG. 2,to allow the fuel 3 to pass through. The size and number of theperforations in the perforated plate 8 are graded so as to allow thedesired ratio of weight of fuel to volume of air to pass through.

The tank 2 is also fitted with an air passage, marked 9 in FIG. 2,providing the lawn mower engine with an air supply. As shown in FIG. 2,this air passage 9 can be a central air passage located on theperforated plate 8.

It may also be located at the side of the perforated plate 8. The airpassage may equally well be located in any other place on condition thatit provides the lawn mower engine with an air supply.

Thus the diameter and/or number of the perforations will be variedaccording to the desired ratio of weight of fuel to volume of air andthe desired flow rate of the fuel.

The tank 2 is located above the carburetor 7 in order to feed it bygravity and air suction. The air/fuel mixture is formed at the pointwhere the air and flour meet downstream, i.e. underneath the perforatedplate 8.

In order to introduce the desired amount of fuel of the invention at thedesired flow rate, it is also necessary to induce the tank 2 to vibrate.

This can be achieved by any appropriate means known to those skilled inthe art. However, in the working tests performed here, this vibration iscreated by placing a weight on the end of the grass cutting blade 6shown in FIG. 1. This weight unbalances the cutting blade 6, therebyinducing the tank 2 to vibrate each time the cutting blade 6 rotates,i.e. each time the engine rotates.

Example 1

Commercial dehydrated chocolate powder was used as fuel for the lawnmower modified as indicated above.

The particle size distribution of this chocolate powder is shown in theform of a curve in FIG. 3 and in the form of numerical values in FIG. 3bis.

Two successive particle size measurements were made on this powder, soFIGS. 3 and 3 bis show the values found for each of these twomeasurements.

In FIG. 3 the first measuring experiment is marked 6015-2. $01 and isshown as a solid line, and the second measuring experiment is marked6015-2 $ 02 and is shown as a broken line.

The average particle diameter of the commercial dehydrated chocolatepowder is 281.2 μm for the first measurement and 357.1 μm for the secondmeasurement.

The median diameter is 290.4 μm in the first experiment and 370.3 μm inthe second experiment.

As can be seen, the average diameter and the median diameter of thispowder are very similar; this indicates a narrow particle sizedistribution, as shown in FIG. 3.

In both the measuring experiments, more than 70% by volume of theparticles of chocolate powder have diameters greater than 150 μm.

The lawn mower ran on this fuel without any problems until thedehydrated chocolate powder contained in the tank 2 was exhausted.

Example 2

The same experiment as in Example 1 was performed except that commercialdehydrated milk powder was used; its particle size was measured as inExample 1.

Also in this case, two particle size measurements were made on thedehydrated milk powder.

The results are shown in FIG. 4 in the form of a curve and in FIG. 4 bisin the form of numerical values. The first measurement is marked 6015-1.$01 and is shown as a solid line in FIG. 4, and the second measurementis marked 6015-1. $ 02 and is shown as a broken line in FIG. 4.

The average diameter of the dehydrated milk particles is 254.4 μm forthe first measurement and 251.5 μm for the second measurement.

The median diameter is 279.1 μm for the first measurement and 272.9 μmfor the second measurement.

Here again, more than 70% by volume of the particles of this milk powderhave a diameter greater than 150 μm.

In the same way as in Example 1, the lawn mower ran until the dehydratedmilk powder contained in the tank 2 was exhausted.

Example 3

The same experiment as in Examples 1 and 2 was performed except that thefine middlings fraction of a wheat flour was used.

The fine middlings fraction of a wheat flour is one of the fractionsnormally rejected after the wheat grains have been ground and screenedin the process for the production of wheat flours for use in food.

The object of the screening operation is to purify the semolinaoriginating from the grinding of the grain.

Two particle size measurements were made on this fine middlingsfraction.

The results of the particle size measurements made on this finemiddlings fraction are shown in FIG. 5 in the form of a curve and inFIG. 5 bis in the form of numerical values. The first measurement ismarked 00. $ 05 and is shown as a solid line in FIG. 5, and the secondis marked 00. $06 and is shown as a broken line in FIG. 5.

The average diameter of this fine middlings fraction is 217.3 μm for thefirst measurement and 218.7 μm for the second measurement.

The median diameter is 222.7 μm for the first measurement and 223.4 μmfor the second measurement.

For this fine middlings fraction, more than 70% by volume of theparticles have a diameter greater than 150 μm.

In the same way, the mower ran until the flour contained in the tank 2was exhausted.

Example 4

The same experiment as in Examples 1, 2 and 3 above was performed exceptthat a coarse middlings fraction of a wheat flour was used.

The coarse middlings fraction of a wheat flour is also one of thefractions normally rejected after the wheat grains have been ground andscreened in the process for the production of a wheat flour for use infood.

The results of the particle size measurements made on this coarsemiddlings fraction are shown in FIG. 6 in the form of a curve and inFIG. 6 bis in the form of numerical values.

Two particle size measurements were made on this coarse middlingsfraction. The first measurement is marked 00. $01 and is shown as asolid line in FIG. 6. The second measurement is marked 00. $02 and isshown as a broken line in FIG. 6.

The average diameter of this coarse middlings fraction is 277.9 μm forthe first measurement and 273.4 μm for the second measurement.

The median diameter is 355.1 μm for the first measurement and 349.0 μmfor the second measurement.

The coarse middlings fraction used in this Example comprises more than70% by volume of particles with a diameter greater than 150 μm.

In the same way as in the previous Examples, the lawn mower ran untilthe flour contained in the tank 2 was exhausted.

Example 5

The same experiment as in Examples 1 to 4 above was performed exceptthat a different coarse middlings fraction of a wheat flour was used.

The results of the particle size measurements made on this coarsemiddlings fraction as shown in FIG. 7 in the form of a curve and in FIG.7 bis in the form of numerical values.

Two particle size measurements were made on this coarse middlingsfraction. The first measurement is marked 00. $03 and is shown as asolid line in FIG. 7. The second measurement is marked 00. $04 and isshown as a broken line in FIG. 7.

The average diameter of the is coarse middlings fraction is 190.2 μm forthe first measurement and 192.2 μm for the second measurement.

The median diameter of the particles of this coarse middlings fractionis 205.6 μm for the first measurement and 206.0 μm for the secondmeasurement.

More than 70% by volume of the particles of this coarse middlingsfraction have a diameter greater than 150 μm.

In the same way as in Examples 1 to 4, the lawn mower ran until theflour contained in the tank 2 was exhausted.

Of course, the invention is in no way limited to the embodimentsdescribed and illustrated, which have been given only as purelyillustrative and non-limiting Examples.

Thus the fuels and fuel mixture of the invention can be used to runinternal combustion engines, such as controlled ignition engines andcompression ignition engines, gas turbines, turbojet engines, ram jetengines and pulse jet engines, i.e. not only motor vehicle engines butalso engines used in the aeronautical sector.

They can also be used in external combustion engines, such as steamturbines and reciprocating steam engines, Stirling cycle engines andstatic engines, such as generator sets or pumps.

Likewise, the fuel and fuel mixture of the invention may be used to runboilers, for example central heating boilers, or furnaces in all typesof industry.

In other words, the invention embraces all the technical equivalents ofthe means described, as well as combinations thereof if these areeffected according to the spirit and scope of the invention as definedin the claims which follow.

In summary, the fuel as defined in the invention can be used as areplacement for liquid, solid or gaseous energy sources such asgasoline, diesel fuel, kerosene, fuel oil, pulverized coal, ordinarycoal, butane, propane, ethanol, methanol, etc.

1. Solid fuel, characterized in that it contains predominantly at leastone constituent which in turn contains: a) predominantly at least onecompound selected from the group comprising starch, lactose, celluloseand derivatives thereof, and b) at least 15% by weight of carbohydrates,based on the total weight of the constituent(s), and in that it is inthe form of a powder whose average particle diameter and median particlediameter are greater than or equal to 150 μm and preferably between 150and 500 μm. 2-13. (canceled)
 14. A method for operating an internalcombustion engine comprising providing to the engine a solid fuelcomprising at least one constituent selected from the group consistingof a cereal flour, a cotton flour, a soybean flour, a potato flour, acassava flour, a dehydrated chocolate powder and a dehydrated milkpowder, said solid fuel being in the form of a powder having an averageparticle diameter and median particle diameter of at least 150 μm. 15.The method according to claim 14, wherein said step of providingcomprises providing more than 70% by volume of said powder of particleswith diameters of at least 150 μm.
 16. The method according to claim 14,wherein said step of providing comprises providing the powder withaverage and median particle diameters between 150 and 500 μm.
 17. Themethod according to claim 15, wherein said step of providing comprisesproviding the powder with average and median particle diameters between150 and 500 μm.
 18. The method according to claim 14, wherein said stepof providing comprises providing the powder with at least oneconstituent selected from the group consisting wheat flour, rye flour,maize flour, barley flour, sorghum flour, foxtail flour, millet flour,oat flour, bran flour, buckwheat flour, corn dredge flour, triticaleflour, rice flour and mixtures thereof.
 19. The method according toclaim 15, wherein said step of providing comprises providing the powderwith at least one constituent selected from the group consisting ofwheat flour, rye flour, maize flour, barley flour, sorghum flour,foxtail flour, millet flour, oat flour, bran flour, buckwheat flour,corn dredge flour, triticale flour, rice flour and mixtures thereof. 20.The method according to claim 14, wherein said step of providingcomprises providing the powder containing cotton flour.
 21. The methodaccording to claim 14, wherein said step of providing comprisesproviding the powder containing soybean flour.
 22. The method accordingto claim 14, wherein said step of providing comprises providing thepowder containing potato flour.
 23. The method according to claim 14,wherein said step of providing comprises providing the powder containingcassava flour.
 24. The method according to claim 14, wherein said stepof providing comprises providing the powder containing dehydratedchocolate powder.
 25. The method according to claim 14, wherein saidstep of providing comprises providing the powder containing dehydratedmilk powder.
 26. The method according to claim 14, wherein said step ofproviding comprises providing the powder containing a mixture of atleast two of a cereal flour, a cotton flour, a soybean flour, a potatoflour, a cassava flour, a dehydrated chocolate powder and a dehydratedmilk powder.
 27. The method according to claim 14, wherein said step ofproviding comprises supplying the fuel in the form of a suspension ofthe powder in air at a concentration of about 200 mg of fuel per literof air.